Impact of Tropical Cyclones on drought alleviation in the Atlantic and Gulf Coasts
Dr. Pat Fitzpatrick of the Stennis Space Center in Mississippi discussed how landfalling tropical storms and hurricanes can alleviate drought. The biggest winner tends to be the Southeast U.S. states of Florida, Georgia, South Carolina, and North Carolina, where about 20% – 50% of all droughts between 1960 – 2009 were busted by a landfalling tropical storm or hurricane. It is uncommon for Texas to see a drought busted; less than 10% of all Texas droughts have been ended by a hurricane or tropical storm. This occurs because the Southeast U.S. can receive heavy rains from hurricanes moving up the East Coast, or moving through the Gulf of Mexico, while relatively few storms track over Texas. Over the course of a year, hurricanes and tropical storms contribute 15 – 20% of rain along the Gulf Coast, and 3 – 16% along the East Coast. The length of a drought does not seem to affect whether a drought can be ended by a hurricane or not. Hurricanes have been able to end both short (< 3 month) and long (> 12 month droughts) equally well.

Figure 1. Example of a drought-busting tropical storm. Moderate drought (Palmer Drought Severity Index, PDSI, ≤ –2.0) was present in 52 percent of the Florida, Georgia, South Carolina, and North Carolina climate divisions in May 2006. The percentage decreased to 29 percent after Tropical Storm Alberto passed through on June 11 – 15, 2006. Image credit: U.S. Drought Monitor.

According to the U.S. drought monitor, over 90% of the area of Florida, Georgia, South Carolina, and North Carolina are currently in moderate to exceptional drought. There is 1 – 2 inches of rain coming to much of the region over the next few days, but that will not be enough to bust the drought. Based on Dr. Fitzpatrick’s research, there is a 20% – 50% chance that the drought will be broken by a tropical storm or hurricane. The first storm on the list in 2012 is Alberto again; let’s hope we get another Alberto this year that imitates the 2006 version of Alberto.

Patterns of rapid intensification
Peter Yaukey of the University of New Orleans studied patterns of hurricane rapid intensification in the Atlantic from 1950 – 2009. The Gulf of Mexico and Caribbean saw the most rapid intensification events, and the Northeast Atlantic the fewest. Interestingly, he found that rapid intensification events did not peak in September, but tended to be more common in June and July. Hurricane are less likely to intensify in the late afternoon and early evening (near 00 UTC), and more likely to intensify just after midnight, at 06 UTC.